Artificial hip joints can comprise a femoral component with a shaft to be inserted into the femur of the patient and an artificial joint ball, as well as an artificial joint socket which is attached to the hip bone of the patient.
In some cases, for example, when the hip prosthesis of a patient has become loose, it may be necessary to perform revision surgery in which the hip joint prosthesis is completely or partially replaced. During partial replacement of the hip joint prosthesis, either the artificial joint socket or the femoral component of the hip joint prosthesis can be replaced.
In particular in revision surgery in which the entire artificial hip joint is replaced, or in surgery where the artificial joint socket is replaced, difficulties can arise due to bone defects in the hip bone of the patient. In view of this situation, special hip implants have been designed for securing an artificial joint socket to the hip bone of a patient in revision surgery.
A modular hip implant according to prior art that can be used in revision surgery, in which the acetabulum of the patient is replaced, is described in WO 2007/118708 A2. The modular hip implant comprises a base that is to be attached to a hipbone and a socket for accommodating a hip joint prosthesis. The base is provided with fastening means for mounting the base on the hipbone as well as a concave receiving area for the socket. The socket has a convex outer form which is complementary to the receiving area such that the radii of curvature determining the concave receiving area and the convex outer form essentially correspond to each other. The socket can be fastened within the base. The base and/or the socket encompass means for adjusting the position of the socket relative to the base. This allows the inclination and the anteversion to be adjusted by suitably arranging the socket in the base. To enable reliably securing the base to the hipbone also in the case of bone defects, cranial plates can be provided having holes into which bone screws can be inserted for screwing the base to the bone of the patient, and a caudal attachment hook can be provided on the base.
While it may be sufficient in some cases to attach the base of the hip implant to the hip bone of the patient and to perform reconstruction of the bone defects of the patient with the help of natural bone material, which can be introduced, for example, through an opening in the base of the hip implant, it can in other cases be advisable to use a so-called augment to fill gaps between the base of the hip implant and the bone of the patient which are caused by bone defects. Such an augment can be formed from metal having a porous structure in order to enhance adherence of the augment to the bone of the patient and it can be attached with the aid of screws and/or bone cement to the hip implant.
It can when using augments be necessary to treat the bone of the patient in order to adapt the shape of the gap between the hip implant and the bone of the patient for accommodating the augment in the gap.
Bone milling devices which are operated by a doctor in an unsupported manner can be used for this purpose. Unsupported milling, however, is tedious and relatively inaccurate, so that there is a risk that too much bone material of the patient is removed.